What is GIS?
What is GIS?
• A technology
– hardware & software tools
– An information handling strategy
• The objective: to improve overall decision making
GIS: a formal definition
“A system for capturing, storing, checking, integrating, manipulating, analysing and displaying data which are spatially referenced to the Earth. This is normally considered to involve a spatially referenced computer database and appropriate applications software”
GIS definition
“… a special case of information system where the database consists of observation son spatially distributed features, activities or events, which are definable in space as points, lines or area. A geographic information systems manipulates data about these points, lines and areas to retrieve data for ad hoc queries and analyses”
Why is GIS unique?
• GIS handles SPATIAL information
– Information referenced by its location in space
• GIS makes connections between activities based on spatial proximity
Characteristics of spatial data
Location
• Description: Kingston University,PenrhynRoad Centre
• Post Code: KT1 2EE
• Grid Reference: 518106.72 168530.37
• Latitude/Longitude: 0° 21’ 55.38”W, 49° 36’ 17.62”N
Geometry
• The shape of a building or county
• The course of a river, the route of a road
• The shape of the landscape, relief
Topology
· Connected to
· Within
· Adjacent to
· North of . . .
· Within the Royal Borough of Kingston-upon-Thames
· Opposite the Surrey County Council building
· North of Surbiton station
· Adjacent to Penrhyn Road
Spatial Data: examples
• Socio-economic data
– Regional health data
– Consumer / lifestyle profiles
– Geodemographics
• Environmental data
– Topographic data
– Thematic data, soils, geology
Spatial data storage
Vector model
• advantage of the vector data format: allows precise representation of points, boundaries, and linear features.
• useful for analysis tasks that require accurate positioning,
• for defining spatial relationship (ie the connectivity and adjacency) between coverage features (topology), important for such purposes as network analysis (for example to find an optimal path between two nodes in a complex transport network)
• main disadvantage of vector data is that the boundaries of the resulting map polygons are discrete (enclosed by well-defined boundary lines), whereas in reality the map polygons may represent continuous gradation or gradual change, as in soil maps.
Raster model
• good for representing indistinct boundaries
• thematic information on soil types, soil moisture, vegetation, ground temperatures
• as reconnaissance satellites and aerial surveys use raster-based scanners, the information (ie scanned images) can be directly incorporated into GIS
• the higher the grid resolution, the larger the data file is going to be
Spatial data storage model
• important in determining the potential applications of the system
• model may also affect the type of analysis work that can be achieved
• hybrid approach to storing graphical and attribute information
• Attribute information often stored within standard relational database
• Graphical information is stored in a proprietary file system
– optimised tools for data handling
– although non-standard proprietary system will be difficult to integrate with other systems, it will tend to be very efficient at handling large graphics files.
